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List Storage Location

A List Storage Location defines where the list records and metadata are stored for an EFP List.

The List Storage Location value is stored in the main EFP List Registry contract and can be changed at any time by the EFP List NFT owner.

Onchain Storage

All EFP data is stored on either Ethereum or a supported L2.

An EFP List can be uniquely specified via three pieces of data:

  • chain_id: The 32-byte EVM chain ID of the chain where the list is stored.
  • contract_address: The 20-byte EVM address of the contract where the list is stored.
  • slot: A 32-byte value that specifies the storage slot of the list within the contract. This disambiguates multiple lists stored within the same contract and de-couples it from the EFP List NFT token id which is stored on Ethereum and inaccessible on L2s.

The following chains are supported:

Chain IDNameLayerType32-Byte Chain ID

More chains will be announced prior to launch.


List Storage Locations are encoded in a versioned, flexible data structure.

Each List Storage Location is encoded as a bytes array with the following structure:

  • version: A uint8 representing the version of the List Storage Location. This is used to ensure compatibility and facilitate future upgrades.
  • location_type: A uint8 indicating the type of list storage location. This serves as an identifier for the kind of data the data field contains.
  • data: A bytes array containing the actual data of the list storage location. The structure of this data depends on the location type.

The version is always 1.

The location type is always 1.

Since only one location type is currently supported, the data field is always a bytes array of length 32 + 20 + 32 = 84.

Location Types

There is only one location type which covers both Ethereum and L2s.

Location TypeDescriptionData
1EVM contract32-byte chain ID + 20-byte contract address + 32-byte slot
2 - 255ReservedN/A


List Storage Location can be represented as a type in any programming language. Here are some examples:


type ListStorageLocation struct {
Version uint8
LocationType uint8
Data []byte


class ListStorageLocation:
version: int # 0-255
location_type: int # 0-255
data: bytes


struct ListStorageLocation {
version: u8,
location_type: u8,
data: Vec<u8>,


* The EFP contracts don't use this struct; they only store list
* storage locations as `bytes` with the version, location type,
* and data fields tightly packed into a single `bytes` value
* however, this struct can be useful for offchain processing with
* foundry or other Solidity tooling
struct ListStorageLocation {
uint8 version;
uint8 locationType;
bytes data;


type ListStorageLocation = {
version: number // 0-255
locationType: number // 0-255
data: Uint8Array